Set 6: Central Ideas (Advanced)
Explanation
PASSAGE
The following text describes a medical breakthrough. Penicillin is a group of antibiotics derived originally from common moulds known as *Penicillium*. Note the discovery of penicillin is attributed to the Scottish scientist Alexander Fleming in 1928. He observed that a mold contaminating a Petri dish of *Staphylococcus* bacteria had killed the bacteria surrounding it. This serendipitous discovery marked the beginning of modern antibiotics, revolutionized medicine, and has saved millions of lives.
How was penicillin discovered, according to the text?
Detailed Explanation
This question asks you to identify the main point of the passage. Choice B is the best answer. The text describes the discovery as 'serendipitous' (accidental) and details how Fleming 'observed that a mold contaminating a Petri dish... had killed the bacteria surrounding it.' This matches Choice B.
Choice C is incorrect because it was accidental, not carefully planned.
Choice D is incorrect because it came from a mold, not factory synthesis (initially).
Choice A is incorrect because herbal remedies are not mentioned. Remember that supporting details help prove the central idea but are not the main point themselves. The author's central idea should be broad enough to encompass the entire passage while still being specific enough to be meaningful. Ask yourself what the author most wants you to understand.
Key Evidence:
• "observed that a mold contaminating a Petri dish... had killed the bacteria"
• "serendipitous discovery"
Why others are wrong: C (Contradicts text - text says serendipitous), D (Irrelevant - text discusses mold origin), A (Irrelevant - not mentioned).
🎯 Keep Practicing!
Master all sections for your best SAT score